1. Field of the Invention
The present invention relates to phosphors, and in particular, relates to a white light illumination device and solar cells utilizing the same.
2. Description of the Related Art
Use of white light emitting diodes (LED) is a new trend in the modern illumination industry due to its energy-saving, low pollution, and long lifetime characteristics. For luminous efficiency of illumination devices, in addition to inherent brightness of LEDs, LED phosphors are also important.
A common commercially available white light LED, uses a blue LED (emission wavelength of 460 nm to 480 nm) collocating with a yellow phosphor, which has poor color-rendering, such that a yellow light may be emitted. Namely, because the intensity of the blue light changes with different input currents, the white light will tend to be yellowish or blueish. Furthermore, because the blue LED chips wear out gradually over time, the white light color may be uneven. To improve color-rendering and luminous efficiency, a UV light emitting diode may be adopted with red, blue, and green phosphors. Because the light source is a UV light, the white light color is not influenced by decreased intensity thereof.
In U.S. Pat. Nos. 7,064,480 and 7,239,082 and World Pat. No. 0211214, a blue-green phosphor aluminate EuMgAl10O17 is disclosed. A phosphor is excited by a major excitation peak of 396 nm to emit a blue-green light having a major emission peak of 477 nm. However, the maximum emission intensity of the phosphor is poor.
Accordingly, the phosphor composition must be tuned to enhance maximum emission intensity. Moreover, emission wavelength of the phosphor must be close to pure blue.